Tuesday, April 17, 2007

Some time ago, when Gardasil was still in clinical trials, I congratulated the Merck team for a product with 100% efficacy. After all, getting anything with 100% efficacy is a rare event, especially in drug/biologic development.

Apparently, that congratulations was a little too soon. Looks like Merck may have found a surrogate endpoint that their vaccine managed very well, but if you look at the important endpoint, the story doesn't look quite so rosy.

So, to be specific, Gardasil is marketed to protect against two strains of human pampilloma virus (HPV) that account for 70% of cervical cancer cases. (Types 16 and 18, for those keeping track.) Merck is going for 80% now by asking the FDA to add types 6 and 11 to the label.

Ed from Pharmalot notes that in clinical trials, among women that already have HPV, the vaccine reduces precancerous lesions (no time limit given) by 14%. For women that don't have HPV, the occurrence of precancerous lesions is reduced 46%. Presumably this is because the vaccine is ineffective against strains that already infect the body. Merck's spin engine is carefully worded to tout that 70%, even though that number is only of secondary importance. It's the 14% and 46% that really matter.

Addendum: I looked at the Gardasil PI, and they already mention 6 and 11. They also mention all other sorts of efficacy measures. The patient product information is less informative. My guess is Merck is overplaying the efficacy in their soundbites by shoving that 70% front and center, but its detractors are overplaying the gap between the 70% and the real story by shoving the 14% front and center.

I'm glad I'm a biostatistician, else I wouldn't be able to understand all this jockeying the numbers.